A projector with rigidly attached camera can be used as a handheld projection system, U.S. patent application Ser. No. 10/394,314 “Geometrically Aware Projector,” filed by Raskar et al., on Mar. 21, 2003, U.S. patent application Ser. No. 10/012,930 “Method for Calibrating a Projector with a Camera,” filed by Raskar et al. on Dec. 10, 2001, and U.S. patent application Ser. No. 10/394,315 “Projector as an input and output device,” filed by Beardsley et al., on Mar. 21, 2003, all incorporated herein by reference, and Raskar et al., “iLamps: Geometrically aware self-configuring projectors, SIGGRAPH Proceedings, 2003.
As the projector projects an output image on a display surface, the camera acquires an input image of the output image. The input image can be used to determine a pose of the projector relative to the display surface. Then, the output image can be adapted to the display surface according to the pose of the projector. For example, it is possible to perform keystone correction.
However, those projector-camera arrangements require that the camera views the entire projected image to extract four vertices in the output image for calibration. More specifically, the camera must view four points projected from known location on the image plane of the projector, e.g., the four corners of the projected image.
This constrains the content of projected images. The projected images cannot have any dark area in the vicinity of the calibration vertices, for example, along the image boundary. The problem is even more difficult when projecting onto a textured surface, rather than a homogeneous surface.
This problem can be solved by also attaching four laser pointers to the projector. Now, the content of the output images do not need to be constrained. In addition, laser light is bright and has a predetermined color, so that the calibration vertices are relatively easy to detect with a camera.
This raises a new problem. Prior art calibration methods assume that the projector and the camera are ‘pinhole’ devices. However, the rays generated by the laser pointers do not necessarily originate at the focal point of the projector. Therefore, the arrangement with laser pointers cannot be treated as a pinhole projection.
Therefore, there is a need to calibrate a projector with laser pointers.